Many of the embodiments in this disclosure relate generally to medical devices, and, more particularly, implantable medical devices (IMDs).
Blood pressure monitoring may be used to assist a medical practitioner in diagnosing cardiovascular and other conditions of a patient. In many instances, blood pressure is monitored indirectly since this technique is relatively non-invasive and is useful for obtaining an approximate blood pressure measurement. In some circumstances, however, a more accurate blood pressure measurement may be needed. In such case, direct blood pressure monitoring, utilizing a device that is surgically implanted into a patient's bloodstream, may be employed.
Some direct pressure monitoring device configurations may include a capsule having a pressure transducer disposed therein. The capsule may include an opening that allows fluid to contact the pressure transducer directly. When the device is appropriately deployed within the patient, blood that is pumped by the heart may exert pressure against the pressure transducer. The pressure transducer may, in turn, sense the exerted pressure and communicate a signal representative of the sensed pressure to a pressure measurement gauge or other appropriate pressure-measuring device.
Such pressure monitoring devices may have disadvantages. For example, because the pressure transducer directly contacts the patient's blood, it may be more susceptible to corrosion. Thus, in cases in which the pressure transducer includes an integrated circuit chip, the device may degrade over time. Furthermore, blood may coagulate around the capsule opening, which may, in turn, affect pressure transducer operation. As a result, there may be difficulties associated with using such pressure monitoring devices for long-term pressure monitoring in an implant environment.
Some pressure monitoring devices may encase a pressure transducer (e.g., a MEMS/IC-type pressure transducer) within a fluid-filled, smooth-surfaced capsule and rigidly attach the pressure transducer to the capsule. In such devices, the pressure transducer is hermetically sealed, and thus not exposed to external media, such as biological fluids. The capsule may include a flexible diaphragm disposed over an opening. When pressure is exerted on the diaphragm, the pressure may be transferred to the pressure transducer via the internal fluid. The pressure transducer may communicate with, e.g., an IMD via a pressure monitoring lead. When such devices are disposed within a patient's heart chamber, heart contractions may cause force to be applied to the lead, thereby applying force directly to the rigidly attached pressure transducer. This strain may decrease the structural integrity of the pressure-monitoring device over time.
Other transducers used in other environments may experience similar issues. Such transducers may include sensing transducers, actuating transducers, IC-only transducers, or combinations thereof, or other suitable transducers.